This invention relates to a bi-directional filter/drier unit, such as may be incorporated in the refrigerant system of a heat pump system or the like, for filtering dirt particles, water, acid and other contaminants from the refrigerant as it flows through the heat pump system. More specifically, the bi-directional filter/drier of the present invention is an improvement of the bi-directional filter/drier unit shown in the co-assigned U.S. Pat. No. 4,125,469 issued Nov. 14, 1978 to Paul V. Henton and Roger J. Fait.
More generally, a heat pump system typically includes a compressor, a pair of heat exchanger coils and appropriate expansion valves incorporated in the refrigerant lines interconnecting the compressor and the heat exchanger coils. Typically, one of the coils is located inside the space to be heated or cooled (e.g., inside a home) and the other is located outside the space (typically, but not necessarily out-of-doors). In its heating mode, high pressure refrigerant is discharged from the output side of the compressor into the inside coil where heat is given off (i.e., the inside coil acts as a condenser). Then, the high pressure liquid refrigerant is directed to the outside coil where it is expanded so as to absorb low grade heat from the outside air. Then, the low pressure refrigerant is returned to the suction side of the compressor. In its cooling mode, the direction of the refrigerant through the system is reversed and the outside coil acts as the condenser and the inside coil acts as an expansion coil.
Typically, filters are provided in the liquid refrigerant lines of the heat pump system so as to filter dirt particles and to absorb water, acid, and other contaminants out of the refrigerant which may harm either the compressor or other components in the system. As noted in the above-mentioned U.S. Pat. No. 4,125,469, heat pumps present special problems to the design of filter/drier units because of the reversal of the direction of the flow of refrigerant causes dirt particles and contaminants entrapped within the filter to be back flushed into the system upon reversal of the direction of flow through the filter. One prior approach was to provide two separate filter/drier units, one operable only during the heating mode of operation of the heat pump and the operable only during the cooling mode. With this filter arrangement, appropriate check valves were provided to prevent reverse flow through the filters. Of course, this arrangement required two separate filter/drier units and required many connections to be made in the heat pump refrigerant system.
The bi-directional filter/drier unit disclosed in the above-noted U.S. Pat. No. 4,125,469 utilizes a flapper valve at each end of a cylindric filter/drier element to admit high pressure refrigerant to the space surrounding the exterior of the filter/drier element. The refrigerant then flows in generally radial direction from the exterior to the interior of the filter/drier element. The refrigerant then flows through an axial bore in the filter/drier element to the opposite end thereof. The filter/drier unit also contains an outlet valve at each end of the filter/drier element so as to permit filtered refrigerant to flow from the filter/drier element. Typically, the flapper valve was made from a limp sheet material, such as a liquid impervious glass fiber cloth or the like. While the above-noted bi-directional filter/drier unit represented a significant advance in the state of the art of bi-directional filter/drier units, and while this bi-directional filter/drier unit did work well for its intended purpose, a problem had been noted that under certain operating conditions, viz, the flapper valve would not, in all cases, sealably close and thus some seepage of refrigerant could occur in reverse direction through the flapper valves.
Among the several objects and features of the present invention may be noted the provision of an improved bi-directional filter/drier unit for a heat pump refrigerant system or the like generally of the type heretofore described in which the flapper valves thereof are held positively closed when in their closed positions and yet which do not unduly restrict the flow of refrigerant therethrough when open; and
The provision of such a bi-directional filter/drier unit which is of simple construction, which is reliable in operation, which is low in cost to manufacture, and which has a long service life.
Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.